EVALUATION OF NOOTROPIC ACTIVITY OF METHANOL STEM EXTRACT OF PARQUETINA NIGRESCENS AFZEL IN MICE

EVALUATION OF NOOTROPIC ACTIVITY OF METHANOL STEM EXTRACT OF PARQUETINA NIGRESCENS AFZEL IN MICE

ABSTRACT

Parquetina nigrescens is a plant with numerous ethnomedicinal uses in African traditional medicine practice. In the South Western part of Nigeria, the stems and roots are roasted, powdered then mixed with pap taken as memory enhancer and for its antiaging effect. This study therefore, aimed to investigate the nootropic activity of the methanol stem extract of P. nigrescens. Phytochemical screening was carried out on the methanol extract and the median lethal dose (LD50) determined using the Organisation for Economic Cooperation and Development in Europe (OECD) 425 limit test. The effect of the extract on cognition was evaluated at doses of 250, 500 and 1000 mg/kg using the elevated plus maze, Barnes maze and novel object recognition test models while the antiamnesic potential was investigated against scopolamine and diazepam induced amnesia. The effect of the extract on exploratory behaviour was also studied using the open field test and hole-board test. The behavioural cognitive enhancing effect of the extract on sub-chronically scopolamine induced cognitive deficit in mice was evaluated in an elevated plus maze and novel object recognition test thereafter, the brain tissue was assayed for malondialdehyde, superoxide dismutase, reduced glutathione and acetylcholinesterase. The results of the phytochemical screening of the extract revealed the presence of carbohydrates, tannins, saponins, phenolics, unsaturated sterols but absence of alkaloids, cardiac glycosides and triterpenes. The LD50 was estimated to be ≥ 5000 mg/kg. Piracetam a standard nootropic agent and the extract decreased transfer latencies at all doses on day 1 and day 2 in the elevated plus maze. In the Barnes maze, the escape latency and escape errors were decreased significantly (p < 0.05, p < 0.01) respectively by the extract at 1000 mg/kg and 250 and 1000 mg/kg respectively. The time spent in target quadrant was significantly (p < 0.01) increased at doses of 250 and 500 mg/kg. Piracetam decreased escape latency, escape errors and increased time spent in target quadrant. Discrimination index in the novel object recognition test was significantly (p < 0.01) increased by piracetam and the extract at all doses tested. Piracetam and the extract at all doses significantly (p < 0.05) decreased the transfer latencies increased by diazepam (0.7 mg/kg) on day 1 and nonsignificantly on day 2 but failed to reverse the scopolamine (1 mg/kg) induced increase in transfer latencies except for piracetam. The extract did not increase number of square cross and rearing, while number of central square cross was significantly (p < 0.01) increased at all doses tested in the open field test. Piracetam increased the number of square, central square cross and rearing. There was significant (p < 0.01) increase in the number of head dip in the hole-board test by the extract which was not observed with piracetam. In the sub-chronic study, piracetam and the extract decreased the transfer latencies on day 1 and 2 in an elevated plus maze and increase discrimination index in the novel object recognition test. The level of malondialdehyde was significantly (p < 0.01) reduced. Piracetam and the extract at all doses tested significantly (p < 0.01) increased superoxide dismutase level. The level of reduced glutathione was non-significantly increased by the extract and piracetam. The activity of the enzyme acetylcholinesterase was not decreased by the extract and piracetam. The methanol stem extract of P. nigrescens possesses nootropic-like activity and antiamnesic effect which may possibly be mediated via inhibition of the GABAergic pathway and this study provides some scientific justification for the ethnomedicinal use of the plant as a memory enhancer.

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